Overtraining Syndrome is a serious problem for athletes and it can afflict runners of all levels. The name is misleading as Overtraining is caused more by lack of recovery rather than too much training. A better name would be "Training Induced Clinical Depression", as Overtraining Syndrome appears to be a type of depression and its effects can last months and sometimes years. A promising training metric for avoiding Overtraining is Training Monotony which looks at how much training varies. There is no good test for Overtraining, but the simplest and possibly most effective is to check Mood State.